Cockroft and Walton Experiment

Converting Mass into Energy

In 1932, the English physicist John Cockroft and the Irish physicist Ernest Walton produced a nuclear disintegration by bombarding Lithium with artificially accelerated protons.

The following reaction took place:

This was the first artificial splitting of a nucleus. It was also the first transmutation using artificially accelerated particles.

Protons were accelerated and slammed into lithium atoms producing alpha-particles and energy. Thus the mass of the proton and lithium was converted into the mass of two alpha-particles and kinetic energy.

This reaction was the first experimental proof of Einstein's E = mc^2

Cockroft and Walton won a Nobel Prize in physics in 1951.

How did it work?

* Transformers, rectifiers and capacitors were used to produce the necessary high d.c. voltage to accelerate the protons.

* Protons produced in a Hydrogen discharge tube were injected into the accelerating tube. Here they were accelerated by the high voltage.

* The protons struck a Lithium target placed at and angle of 45 degrees to the beam

* The products of the reaction were emitted at right angles to the proton beam and struck Zinc sulphide screens producing small flashes of light called scintillations which could be seen with a microscope

* It was shown that the products were Helium nuclei (i.e. alpha-particles), emitted in opposite directions with the same speed.

A transmutation is the changing of a nucleus of one atom into a nucleus with a different atomic number (i.e. the changing of an atom of one element into an atom of another element)